Smoking article with mercaptopropyl functionalized sorbent and method

ABSTRACT

Mercaptopropyl functionalized molecular sieves such as mesoporous SBA-15 silica molecular sieves can be prepared via incipient-wetness impregnation of (3-mercaptopropyl)triethoxysilane of up to a loading of about 15 mole %. The functionalized materials are more hydrophobic than parent material, and can be used as adsorbents to reduce the concentration of heavy metal (mercury and/or cadmium-containing) constituents in mainstream smoke. For example, SBA-15 silica comprising a 1% molar loading of mercaptopropyl groups has an adsorption capacity for mercury that is approximately seven to eight times that of un-functionalized parent SBA-15 silica.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Application No. 60/613,513 filed on Sep. 28, 2004, theentire content of which is incorporated herein by reference.

BACKGROUND

In the description that follows reference is made to certain structuresand methods, however, such references should not necessarily beconstrued as an admission that these structures and methods qualify asprior art under the applicable statutory provisions. Applicants reservethe right to demonstrate that any of the referenced subject matter doesnot constitute prior art.

SUMMARY

Cigarette filters and smoking articles such as cigarettes, pipes, cigarsor non-traditional cigarettes comprise a sorbent having mercaptopropylgroups bound to an inorganic molecular sieve substrate, wherein thesorbent is capable of reducing the concentration of at least one heavymetal constituent in mainstream smoke. Preferably, the sorbent isincorporated in an amount effective to reduce levels of mercury and/orcadmium in mainstream smoke.

The inorganic molecular sieve substrate can comprise mesoporous ormicroporous molecular sieves. Exemplary molecular sieve substratematerials include zeolites, silicates such as mesoporous silicates,aluminophosphates, mesoporous aluminosilicates, and mixtures thereof.Zeolites can include zeolite ZSM-5, zeolite A, zeolite X, zeolite Y,zeolite K-G, zeolite ZK-5, zeolite Beta, zeolite ZK-4, and mixturesthereof. When incorporated in a smoking article or in a cigarettefilter, the sorbent preferably has a particle size from about 20 mesh toabout 60 mesh.

One preferred sorbent comprises (3-mercaptopropyl) silane covalentlybound to a zeolite. A further preferred sorbent comprises(3-mercaptopropyl) silane covalently bound to a mesoporous silicate.SBA-15 silica, for example, is a mesoporous molecular sieve that canhave incorporated therein up to about 15 mole percent of(3-mercaptopropyl) trialkoxysilane with respect to silicon in theSBA-15.

Preferably, the mercaptopropyl groups are covalently bound to exteriorand interior surfaces of the inorganic molecular sieve substrate.Smoking articles and filters can comprise from about 10 mg to about 300mg or from about 100 mg to about 200 mg of the sorbent, and the sorbentis preferably in granular form having a particle size from about 20 meshto about 60 mesh.

Preferred cigarette filters comprise mono filters, dual filters, triplefilters, cavity filters, recessed filters and free-flow filters.Further, the cigarette filter can comprise cellulose acetate tow,cellulose paper, mono cellulose, mono acetate, and combinations thereof.The sorbent can be incorporated into one or more cigarette filter partssuch as a shaped paper insert, a plug, a space, cigarette filter paper,and a free-flow sleeve. As an example, the sorbent can be incorporatedwith cellulose acetate fibers or polypropylene fibers forming a plug ora free-flow filter element.

In an embodiment, the sorbent can be incorporated in at least one of amouthpiece filter plug, a first tubular filter element adjacent to themouthpiece filter plug, and a second tubular filter element adjacent tothe first tubular element. In a further embodiment, the sorbent can beincorporated in at least one part of a three-piece filter including amouthpiece filter plug, a first filter plug adjacent to the mouthpiecefilter plug, and a second filter plug adjacent to the first filter plug.

A method of making a cigarette filter comprises incorporating a sorbentinto a cigarette filter, wherein the sorbent comprises mercaptopropylgroups bound to an inorganic molecular sieve substrate. As used herein,“MTP” denotes the mercaptopropyl group, and unless otherwise stated thepercent loading of mercaptopropyl groups on a substrate is given in molepercent.

A method of making a cigarette comprises (i) providing a cut filler to acigarette making machine to form a tobacco column; (ii) placing a paperwrapper around the tobacco column to form a tobacco rod; and (iii)attaching a cigarette filter comprising the sorbent to the tobacco rodusing tipping paper.

A method of treating tobacco smoke comprises contacting mainstreamtobacco smoke with a sorbent having at least one mercaptopropyl groupbound to an inorganic molecular sieve substrate while drawing mainstreamtobacco smoke through a smoking article, wherein the sorbent reduces theconcentration of at least one heavy metal constituent in mainstreamsmoke.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an adsorption-desorption isotherm of argon at about 87 Kfrom SBA-15 (8% MTP), where 8% denotes the molar loading ofmercaptopropyl groups on a molecular sieve substrate comprising SBA-15mesoporous silica. The inset shows the corresponding pore sizedistribution of the sorbent material.

FIG. 2(a) shows a TEM image in the direction of a pore axis and FIG.2(b) shows EELS imaging of sulfur in SBA-15 (8% MTP).

FIG. 3 shows FTIR spectra in the hydroxyl stretching range of (a) parentSBA-15 silica, (b) SBA-15 (1% MTP), (c) SBA-15 (2% MTP), (d) SBA-15 (4%MTP), (e) SBA-15 (8% MTP) and (f) SBA-15 (16% MTP).

FIG. 4 shows single-pulse ²⁹Si MAS NMR spectra of (curve a1) parentSBA-15 silica and (curve b1) SBA-15 (16% MTP). Curves (a2) and (b2) arethe corresponding ²⁹Si MAS NMR spectra with ¹H cross polarization of thesame materials.

FIG. 5 is a ¹³C MAS NMR spectrum of SBA-15 (16% MTP).

FIG. 6 shows ¹H MAS NMR spectra of (a) parent SBA-15 silica and (b)SBA-15 (16% MTP).

FIG. 7 shows TGA and DTG curves of (a) parent SBA-15 silica, (b) SBA-15(1% MTP), (c) SBA-15 (2% MTP), (d) SBA-15 (4% MTP), (e) SBA-15 (8% MTP),(f) and (f′) SBA-15 (16% MTP).

FIG. 8 shows mercury breakthrough of each mercury vapor pulse flowingthrough (●) cellulose acetate fibers only, (▾) parent SBA-15 silica, (♦)SBA-15 (1% MTP), (⋄) SBA-15 (2% MTP), (▴) SBA-15 (4% MTP) and (∘) SBA-15(8% MTP).

FIGS. 9-11 show various cigarette embodiments in which a sorbentcomprising at least one mercaptopropyl group bound to an inorganicmolecular sieve substrate can be incorporated.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Smoking articles, cigarette filters and methods for making cigarettefilters comprise a sorbent that is adapted to reduce the concentrationof at least one heavy metal constituent from the mainstream smoke of acigarette. The sorbent comprises an inorganic molecular sieve substratehaving mercaptopropyl (MTP) groups bound thereto.

The molecular sieve substrate can comprise a microporous or a mesoporoussubstrate. Microporous substrates have an average pore size of less thanabout 2 nm (20 Å), and mesoporous substrates have an average pore sizeof from about 2 nm to 50 nm (20 to 500 Å). The substrate can be anatural or a synthetic material. Exemplary substrates include zeolites,aluminophosphates, mesoporous silicates, mesoporous aluminosilicates,and mixtures thereof. Mesoporous silica molecular sieves, for example,can have an internal surface area of around 1000 m²/g and uniformmesopore channels. The sorbent can be used to adsorb molecules attemperatures up to about 700° C. or more.

Mercaptopropyl groups can be incorporated into a molecular sievesubstrate via a direct synthesis route involving the co-condensation oftetraethoxysilane and (3-mercaptopropyl)triethoxysilane followed bypost-synthesis acid or alcohol extraction of the structure-directingagent used in the synthesis. As an alternative, mercaptopropyl groupscan be incorporated into molecular sieve substrates by refluxing asubstrate material such as freshly calcined particles of mesoporoussilica in dry toluene containing (3-mercaptopropyl)triethoxysilane. Themercaptopropyl groups can be transformed to alkylsulfonic acid groupsvia mild oxidation with hydrogen peroxide solution and furtheracidification.

A preferred substrate material is a SBA-15 silica molecular sieve.SBA-15 silica molecular sieve is a mesoporous molecular sieve having auniform pore size of between about 5 to 20 nm and a mean surface area ofabout 200-230 m²/g.

As described herein, the mesoporous SBA-15 silica molecular sieves canbe functionalized with mercaptopropyl functional groups in an effectiveamount, preferably in an amount of up to 15 mole % compared to theparent SBA-15. The incorporated mercaptopropyl groups are uniformlydispersed, and chemically bonded to surface silicon associated with thesilanol groups in the parent SBA-15. The functionalized materials retainthe well-defined mesoporosity of the SBA-15 silica, and can adsorb traceamounts of heavy metal vapor.

The incipient-wetness method is a preferred method of incorporatingmercaptopropyl groups in a molecular sieve substrate material. SBA-15silica molecular sieve (hereinafter SBA-15) can be functionalized withmercaptopropyl groups via incipient-wetness impregnation of(3-mercaptopropyl)triethoxysilane at elevated temperature using drytoluene. According to a preferred method, the SBA-15 is pre-calcined inair at 550° C. for 24 hours and then added to a dry toluene solutioncontaining dissolved (3-mercaptopropyl)triethoxysilane followed byvigorous shaking at room temperature. The(3-mercaptopropyl)triethoxysilane concentration in the solution can varyfrom about 0.017-0.267 M, and the amount of SBA-15 and/or the amount ofthe toluene solution can be selected depending on the desired loading ofmercaptopropyl groups. The mixture of SBA-15 and(3-mercaptopropyl)triethoxysilane can be heated (e.g., at 100° C. for 24h), filtered, and washed with dry toluene followed by dichloromethane,and then dried at 120° C. for 12 h. The sorbent materials made usingthis method are designated SBA-15 (MTP-X), where MTP denotes themercaptopropyl group and X is the molar percent of(3-mercaptopropyl)trialkoxysilane added to the toluene solution withrespect to silicon in the parent SBA-15 material.

Characterization data for the SBA-15 (MTP-X) material are shown in FIGS.1-8. Powder x-ray diffraction (XRD) patterns from 0-15° (2θ) were takenby IC Laboratories, Amawalk, N.Y. Transmission electron microscopy (TEM)and electron energy loss spectroscopy (EELS) measurements were conductedwith an FEI Technai F20 field emission electron microscope operating atan accelerating voltage of 200 kV. EELS spectra and images werecollected with a Gatan Imaging Filter and analyzed with Gatan DigitalMicrograph software. Fast Fourier Transforms (FFT) of the images werealso calculated with the Gatan Digital Micrograph software. EELS imagesof sulfur were collected by measuring the intensity from a windowspanning the S_(L) edge and subtracting the intensity extrapolated fromtwo pre-edge windows. A similar process using the C_(K) edge was usedfor carbon imaging.

Argon adsorption isotherms were measured at 87.29 K using aMicromeritics ASAP 2010 analyzer. The specific surface area, A_(BET),was determined from the linear part of the Brunauer, Emmett, and Teller(BET) equation (P/P₀=0.05-0.31). The calculation of pore sizedistribution was performed using the desorption branch of an argonadsorption isotherm and the Barrett-Joyner-Halenda (BJH) formula. Thecumulative mesopore surface area, A_(BJH), and volume, V_(BJH), wereobtained from the pore size distribution curves. The average mesoporouspore diameter, D_(BJH), was calculated as 4V_(BJH)/A_(BJH).

Thermogravimetric analysis (TGA) was carried out on a TA Instruments2950 Thermogravimetric Analyzer in helium at a heating rate of 10°C./min. The weight loss was normalized to the sample weight at 100° C.and plotted versus temperature as thermogravimetric (TG) anddifferential thermogravimetric (DTG) curves.

Fourier-transform infrared spectroscopy (FTIR) spectra were recorded ona MIDAC Corporation 2100 spectrophotometer, with a resolution of 0.5cm⁻¹ equipped with a mercury-cadmium-telluride (MCT) detector.Measurements were conducted in reflectance mode using a Spectral-TechTemperature/Vacuum chamber with potassium bromide (KBr) windows, whichwas mounted to a Spectral-Tech collector in the infrared beam.

Solid-state magic-angle-spinning (MAS) NMR spectra were recorded at 4.7Tesla using a Varian Unity-200 spectrometer equipped with a DotyScientific high-speed multinuclear MAS probe. ²⁹Si MAS spectra weremeasured at 39.7 MHz, with 30° pulses and 90 sec recycle delays using 7mm silicon nitride rotors spinning at 8.2 kHz. ¹H-²⁹Sicross-polarization (CP) MAS NMR spectra were also recorded utilizing 7mm silicon nitride rotors spinning at 8.2 kHz. The cross-polarizationcontact time was 3 ms, and the pulse repetition rate was 3 sec. The 50.3MHz ¹³C CP MAS NMR spectra were obtained with a 750 μsec contact timeand a 2.5 sec pulse repetition rate using silicon nitride rotors at thesame spinning speed. The 200 MHz ¹H MAS NMR spectra were also obtainedat a spinning speed of 8.2 kHz with a 2 sec pulse repetition rate. Thechemical shifts are reported in ppm relative to externaltetramethylsilane (TMS) for ¹H, ¹³C, and ²⁹Si.

To evaluate the adsorption efficiency of the sorbent material, agranular sample of the sorbent material was loaded into a sample tube.The granular sample was prepared by first pressing a pellet of thesorbent material (1000 kg force in a 31 mm inner diameter die) and thencrushing and sieving the pellet to recover particles having an averagesize in the range of about 0.3-0.8 mm. In a typical experiment, about 50mg of sorbent particles were placed into a polypropylene sample tube of6 mm inner diameter and both ends of the tube were blocked withcellulose acetate fibers. A blank (i.e., reference) sample tube wassimilarly prepared but without adding any sorbent material.

Mercury uptake (mercury adsorption) measurements were carried out byinjecting 7 ng pulses of elemental mercury vapor in a nitrogen carriergas flowing through the sample tube at a constant flow rate of 70cc/min. The breakthrough mercury (i.e., un-adsorbed mercury that passedthrough the tube) was collected by a gold trap and analyzed by coldvapor atomic absorption spectrometry (CVAAS) using a Perkin Elmer FIASequipped with an amalgam system accessory and interfaced to a PerkinElmer 4100ZL spectrometer. Multiple pulses of mercury vapor were dosedin sequence and analyzed individually for mercury breakthrough.

Both the parent and the mercaptopropyl-functionalized SBA-15 havewell-resolved XRD patterns with a prominent peak at 0.8°, and two weakpeaks at 1.6° and 1.7°, which match well with those reported for SBA-15.The SBA-15 can be indexed to a hexagonal lattice with a d(100)-spacingof 99.1 Å, which corresponds to a unit cell parameter, a₀˜114 Å, wherea₀=2d(100)/√3).

FIG. 1 shows a typical argon adsorption-desorption isotherm of themercaptopropyl-functionalized SBA-15. The functionalized material (8%MTP) exhibits an irreversible type IV adsorption isotherm with an H1sorption hysteresis loop as defined by the International Union of Pureand Applied Chemistry (IUPAC) classification scheme and is substantiallyidentical in its overall adsorption-desorption profile to the parentSBA-15. A corresponding BJH plot based on the isotherm is shown in theinset for FIG. 1. From the BJH plot, the sorbent material has a narrowpore size distribution with a predominant mesopore size of about 55 Å.

With an increase in the loading of mercaptopropyl groups, a shift inhysteresis toward low relative pressure and a slight decrease in overallargon adsorption volume are observed. The calculated pore structureparameters, summarized in Table 1, show a trend of slightly decreasingsurface area, pore volume and pore diameter with increased loading ofmercaptopropyl groups. TABLE 1 Pore structure parameters ofMTP-functionalized SBA-15 A_(BET) Material (m²/g) A_(BJH) (m²/g) V_(BJH)(cm³/g) D_(BJH) (nm) SBA-15 704 685 1.12 6.53 SBA-15 (1% MTP) 589 6760.97 5.74 SBA-15 (2% MTP) 640 733 1.10 5.98 SBA-15 (4% MTP) 578 665 0.975.82 SBA-15 (8% MTP) 467 542 0.71 5.27 SBA-15 (16% MTP) 374 447 0.565.03

TEM images of parent SBA-15 material and mercaptopropyl groupfunctionalized SBA-15 (8% MTP) reveal hexagonal arrays of uniformchannels of about 6 nm in diameter (FIG. 2 a). Line spacing from the FFTshow d-spacings ranging from 8-10 nm, indicating that slightly less thanhalf of this spacing is wall material with the remainder being voidspace. The TEM image of the functionalized material also illustrates atightly packed hexagonal silica grain, which mimics individual porechannels of the SBA-15.

As revealed by XRD, TEM, and argon adsorption measurements, themercaptopropyl group functionalized SBA-15 has a uniform mesoporousstructure with a narrow pore size distribution and a high surface areainherited from the parent SBA-15 silica. The average pore dimensionshrinks slightly due to occupation of the incorporated mercaptopropylgroups. It is apparent that the inorganic wall structure of the SBA-15silica remains intact during the modification process.

EELS imaging of sulfur in the mercaptopropyl group functionalized SBA-15show a uniform distribution of the functional groups within the SBA-15matrix (FIG. 2 b). This suggests that the functional groups penetratedthe entire depth of the channels. Sulfur is substantially absent fromthe channel walls.

The FTIR spectrum in the hydroxyl stretching range of the parent SBA-15shows a narrow and intense band at 3740 cm⁻¹ and a broad low-frequencyband centered at 3400 cm⁻¹ (FIG. 3 a). The narrow band at 3740 cm⁻¹ isdue to the stretching vibration mode of isolated terminal silanol(Si—OH) groups, while the broad low-frequency band at 3400 cm⁻¹corresponds to adsorbed water, silanol groups and the hydrogen-bondinginteraction there between.

For the mercaptopropyl group functionalized SBA-15, both bands at 3740cm⁻¹ and 3400 cm⁻¹ decrease in intensity with increasing mercaptopropylgroup loading (FIG. 3(b)-(f). The presence of mercaptopropyl groups isidentified by the appearance of the C—H stretching bands at 2927 cm⁻¹and 2857 cm⁻¹.

The ²⁹Si MAS NMR spectrum of the parent SBA-15 is broad and dominated byan intense line at −107 ppm along with two shoulders at −98 and −89 ppm(FIG. 4, curve a1). The latter two shoulders at −98 and −89 ppm appearin increased intensity in the spectrum with ¹H cross-polarization (FIG.4, curve a2), which may indicate a close location of these silicon atomsto protons. By analogy, the chemical shift at −107 ppm for zeolites andamorphous silica materials can be assigned to Si(OSi)₄ (Q4,Q_(n)=Si(OSi)_(n)(OH)_(4-n), n=2−4) structural units, and the lines at−98 and −89 ppm can be assigned to Si(OSi)₃OH (Q3) and Si(OSi)₂(OH)₂(Q2) structural units, respectively. The Q4 structural units representregularly interlinked SiO₄ tetrahedra in the interior of the mesoporewalls, while Q3 and Q2 structural units are present on the wall surface,i.e., associated with silanol groups.

In contrast to the parent SBA-15 silica, the ²⁹Si MAS NMR spectra of themercaptopropyl group functionalized SBA-15 show only a broad linecentered at −107 ppm due to Q4 structural units. The lines at −98 and−89 ppm, which are due to Q3 and Q2 structural units, are missing evenin the spectrum with ¹H cross-polarization (FIG. 4, curves b1 and b2).Three additional lines at −47, −57 and −66 ppm appear and theirintensity is enhanced by ¹H cross-polarization (FIG. 4, curves b1 andb2). This indicates formation of new siloxane linkages (Si—O—Si) ofmercaptopropylsilane silicon to the surface silicons of the SBA-15silica. The line at −66 ppm is associated with silicon ofmercaptopropylsilane attached via three siloxane bonds,(—O—)₃SiCH₂CH₂CH₂SH (T3, T_(m)=RSi(OSi)_(m)(OR′)_(3-m), m≦3, where R andR′=H or a hydrocarbon chain), while the lines at −57 ppm and −47 ppm areassociated with silicon attached via two siloxane bonds(—O—)₂SiCH₂CH₂CH₂SH (T2), and one siloxane bond, (—O—)SiCH₂CH₂CH₂SH(T1), respectively.

The ¹³C MAS NMR spectra of the mercaptopropyl group functionalizedSBA-15 reveal three well-resolved lines at 49, 27 and 10 ppm (FIG. 5).These lines can be assigned to the C3, C2, and C1 carbons of theincorporated mercaptopropyl groups, (—O—)₃SiCH₂(1)CH₂(2)CH₂(3)SH,respectively. No lines at 59 ppm and 16 ppm due to residual ethoxycarbon are observed.

The ¹H MAS NMR spectrum of the parent SBA-15 silica (FIG. 6 a) shows anarrow line at 1 ppm embedded in the central part of an extremely broadline spanning the entire range of chemical shifts due to various secondorder nuclear spin interactions. Because of the siliceous nature of thematerial, these lines are likely associated with the protons of thesilanol groups on the internal surface of the SBA-15 silica.

By contrast, ¹H MAS NMR spectra of the mercaptopropyl groupfunctionalized SBA-15 show a wider range of chemical shifts with anumber of resolved lines at 0, −1, −4 ppm (FIG. 6 b), but not at 1 ppm.These lines are apparently due to the protons in the side chains of theincorporated mercaptopropyl groups.

The parent SBA-15 silica shows a constant but slight weight loss withincreasing temperature (FIG. 7 a, Table 2), which can be due to surfacedehydration and/or dehydroxylation. In contrast, the mercaptopropylgroup functionalized SBA-15 shows a progressive weight loss (FIG. 7 b-7f), apparently due to decomposition of the mercaptopropyl groups. Thedecomposition temperature, identified in the DTG curve (FIG. 7 f′), isapproximately 300° C., which is well above the boiling point of thesource liquid (3-mercaptopropyl)triethoxysilane. The molar weight losscalculated from the total weight loss (Table 2) agrees well with theamount of mercaptopropyl groups added to the impregnation solution overthe range of 1-8 molar % (calculated with respect to silicon in theparent SBA-15 silica). However, the total molar weight loss for thesample with the highest molar loading (16%) was 14.8%. Themercaptopropyl group functionalized SBA-15 samples were observed to bemore hydrophobic showing less weight loss upon thermal treatment fromroom temperature to 100° C. as compared with the parent SBA-15 silica,indicating improved hydrophobicity.

As evidenced by EELS imaging of sulfur, FTIR, and ¹H, ¹³C and ²⁹Si MASNMR spectra, the incorporated mercaptopropyl groups are uniformlydispersed over the SBA-15 silica particles and chemically bonded to theinternal surface of the channels of the SBA-15. This may account for theincreasing immobility and thermal stability of the incorporatedmercaptopropyl groups in comparison with the neat(3-mercaptopropyl)triethoxysilane liquid. The observed improvedhydrophobicity of the mercaptopropyl group functionalized SBA-15suggests that the sorbent material can be used in a high humidityenvironment.

Spectra from FTIR, ¹H and ²⁹Si MAS NMR measurements provide informationregarding the nature of the attachment and bonding patterns of themercaptopropyl groups to the internal surface of the SBA-15 silica. Theparent SBA-15 silica possesses abundant silanol groups which line thetubular channels, as evidenced by the intensive hydroxyl stretchingbands in the FTIR spectra as well as by the well-resolved resonancelines of Q3 and Q2 structural units in the ²⁹Si CP MAS NMR spectra. Thesilanol groups are apparently located in a relatively uniform chemicalenvironment with some mobility, as indicated by the well-resolved andnarrow line in the ¹H MAS NMR spectrum. These spectral features becomeless predominant and disappear upon incorporation of the mercaptopropylgroups, suggesting that the surface silanol groups serve as sites foranchoring the mercaptopropyl groups and are consumed. The most probablemechanism for the attachment of the mercaptopropyl groups to theinternal surface of the parent SBA-15 silica is through one, two, orthree siloxane linkages (Si—O—Si) connecting a mercaptopropylsilanesilicon to the surface silicon atoms of the SBA-15 material. Such asiloxane linkage may also occur between neighboring mercaptopropylsilanesilicon atoms. A wider range of chemical shifts or the broad line shapeof the ¹H MAS NMR spectra of the mercaptopropyl group functionalizedSBA-15 silica suggest that mercaptopropyl groups are present in avariety of configurations, which restricts their free mobility orrotation.

In addition, ¹³C MAS NMR confirmed that the structure of themercaptopropyl groups remain intact during the incorporation process.The lack of resonance lines of any residual ethoxy groups indicate acomplete hydrolysis and/or condensation of the mercaptopropylsilane.This suggests that the synthesis method is effective in incorporatingmercaptopropyl groups into the SBA-15 silica.

SBA-15 silica functionalized with mercaptopropyl groups can be used asan adsorbent to reduce the concentration of heavy metals (e.g., heavymetal vapors). The adsorbent properties of the functionalized mesoporousSBA-15 silica molecular sieves are inherited from both the inorganicsupport and the organic moieties. The mesoporous silica frameworkprovides uniform and controlled mesoporosity, whereas the incorporatedmercaptopropyl groups define interfacial and bulk characteristics, suchas the environment of adsorption sites and the hydrophobicity associatedwith the alkyl chains.

FIG. 8 shows mercury breakthrough for a sequence of 7 ng pulses ofelemental mercury vapor entrained in nitrogen and flowed over samples of(●) cellulose acetate fibers only, (▾) parent SBA-15 silica, (♦) SBA-15(1% MTP), (⋄) SBA-15 (2% MTP), (▴) SBA-15 (4% MTP) and (∘) SBA-15 (8%MTP). The corresponding total mercury uptake in the first four pulsesare integrated and summarized in Table 2. The blank sample tube filledonly with cellulose acetate fibers did not show any notable reduction inmercury breakthrough, suggesting that the uptake of mercury vapor by thecellulose acetate fibers is negligible.

For the parent SBA-15, a small reduction in mercury breakthrough wasobserved only in the first pulse, but not in subsequent pulses. Bycontrast, the functionalized SBA-15 (1% MTP) shows a substantialreduction in mercury breakthrough of about 24% in the first pulse withdecreasing, yet significant levels in the subsequent pulses. Thecalculated total mercury uptake for the SBA-15 (1% MTP) sorbent isbetween about seven to eight times greater than the uptake for theparent SBA-15 silica (Table 2). However, as the molar percentage loadingof mercaptopropyl groups in the functionalized SBA-15 increases, thedata in FIG. 8 show a trend of declining levels of the reduction inmercury breakthrough versus increasing loading of mercaptopropyl groups.

The data from TGA measurements indicate that the mercaptopropyl groupscan be incorporated into the SBA-15 silica via incipient-wetnessimpregnation up to a molar percentage loading of about 15% verses theparent SBA-15 silica. The incorporated mercaptopropyl silane groups arechemically bonded to surface silicons associated with the silanol groupsof the parent SBA-15 silica and remain intact during various stages ofthe preparation. Specifically, the channels of the SBA-15 silica can beuniformly lined with mercaptopropyl groups up to a molar percentageloading of about 15% while retaining the original mesoporosity.

Because the pore dimension of the SBA-15 silica is only slightlynarrowed after functionalization with the mercaptopropyl groups (Table1), and because most heavy metal elements such as mercury have a smallatomic size (e.g., about 1.5 Å diameter), such a decrease in mercurybreakthrough at higher loadings is not likely caused by steric effects.Without wishing to be bound by theory, it is anticipated that at higherloadings the incorporated mercaptopropyl groups align into aconfiguration with significant hydrogen bonding interaction among thetails of the functional groups, which may cause a reduction in theiradsorption capacity. Such an alignment mechanism suggests that isolatedmercaptopropyl groups on the internal surface of the SBA-15 silica mayserve as preferred adsorption sites for heavy metal (e.g., mercury)vapor. TABLE 2 Mercaptopropyl group content and total mercury uptake ofMTP-functionalized SBA-15 Weight loss MTP molar content Mercury uptakeMaterial (wt. %) (wt. %) (ng/g) SBA-15 0 n/a 11.0 SBA-15 (1% MTP) 1.00.8 80.6 SBA-15 (2% MTP) 2.1 1.7 66 SBA-15 (4% MTP) 4.6 4.0 59.2 SBA-15(8% MTP) 10.1 9.9 25.4 SBA-15 (16% MTP) 13.9 14.8 n/a

In Table 2, the total weight loss is determined from TGA measurements at800° C. and normalized to the weight loss for SBA-15. The total weightloss, assuming complete decomposition of MTP at 800° C., is used todetermine the MTP content in each sample. The measured value for mercuryuptake was based on the total mass of the material.

As shown in Table 2, mercaptopropyl group functionalized SBA-15 can bean effective adsorbent for elemental mercury vapor from a gas stream ascompared with the parent SBA-15. However, the decreased adsorptionefficiency and capacity at the higher loading levels of mercaptopropylgroups implies that not only the mercaptopropyl groups, but also theinterfacial properties on the internal surface of the functionalizedSBA-15 can influence adsorption performance.

In a separate test, a cigarette tobacco smoke stream containing bothparticulate matter and volatile constituents was injected in eight 2second 35 ml pulses at intervals of 60 seconds into an 8 mm sample tubecontaining 0.037 g of SBA-15 (8% MTP) material. The tobacco smoke streamcomprised 5.3 ng arsenic, 61.8 ng cadmium, 4.9 ng mercury, about 10 ngnickel, 36.1 ng lead, and 1.86 ng selenium. The result showed a 44%reduction in cadmium breakthrough.

FIG. 9 depicts a traditional lit end cigarette comprising a filter 10,tobacco rod 12, and tipping paper 14. See, for example, the filterconstructions in FIGS. 1-7 of commonly-owned U.S. Pat. No. 6,595,218,the disclosure of which is hereby incorporated by reference. The filter10 can have any desired construction wherein the sorbent is incorporatedtherein.

FIG. 10 depicts an electrically heated smoking system 20 comprising aspecially constructed cigarette 22 and an electrical lighter 24, thecigarette 22 including a filter portion 26 and a tobacco rod portion 28.When inserted in lighter 24, the cigarette releases tobacco flavor andaroma as a result of heater blades heating the cigarette along charlines 29. See, for example, commonly-owned U.S. Pat. No. 5,692,529, thedisclosure of which is hereby incorporated by reference. The filterportion 26 can have any desired construction wherein the sorbent isincorporated therein.

FIG. 11 depicts a smoking article 30 having a filter 32, tobacco bed 34and heating element 36 at the end of bed 34. See, for example,commonly-owned U.S. Pat. No. 4,966,171, the disclosure of which ishereby incorporated by reference. When drawn upon, heat from the heatingelement 36 heats the bed of tobacco to release tobacco flavors andaromas. The filter 32 can have any desired construction wherein thesorbent is incorporated therein.

In preferred embodiments, the sorbent can be incorporated in a smokingarticle such as traditional or non-traditional cigarettes, or incigarette filters. Smoking articles and cigarette filters comprisingsorbent media and methods of incorporating sorbent media in cigarettesand in cigarette filters are disclosed in commonly-owned U.S. Pat. No.6,814,786 and in commonly-owned U.S. Patent Publication No.2003/0159703, the contents of which are herein incorporated byreference.

All of the above-mentioned references are herein incorporated byreference in their entirety to the same extent as if each individualreference was specifically and individually indicated to be incorporatedherein by reference in its entirety.

While the invention has been described with reference to preferredembodiments, it is to be understood that variations and modificationsmay be resorted to as will be apparent to those skilled in the art. Suchvariations and modifications are to be considered within the purview andscope of the invention as defined by the claims appended hereto.

1. A smoking article comprising a sorbent having mercaptopropyl groupsbound to an inorganic molecular sieve substrate, wherein the sorbent iscapable of reducing the concentration of at least one heavy metalconstituent in mainstream smoke.
 2. The smoking article of claim 1,wherein the smoking article is selected from the group consisting of acigarette, a pipe, a cigar and a non-traditional cigarette.
 3. Thesmoking article of claim 1, wherein the sorbent is located in a filterselected from the group consisting of a mono filter, a dual filter, atriple filter, a cavity filter, a recessed filter, and a free-flowfilter.
 4. The smoking article of claim 1, wherein the heavy metalconstituent comprises mercury and/or cadmium.
 5. The smoking article ofclaim 1, wherein the inorganic molecular sieve substrate (a) comprisesmesoporous or microporous molecular sieves; (b) is selected from thegroup consisting of a zeolite, silicate, aluminophosphate, mesoporoussilicate, mesoporous aluminosilicate, and mixtures thereof; or (c)comprises a zeolite selected from the group consisting of zeolite ZSM-5,zeolite A, zeolite X, zeolite Y, zeolite K-G, zeolite ZK-5, zeoliteBeta, zeolite ZK-4, and mixtures thereof.
 6. The smoking article ofclaim 1, wherein the sorbent comprises (a) (3-mercaptopropyl)silanecovalently bound to a zeolite; (b) SBA-15 silica having incorporatedtherein up to about 15 mole percent of (3-mercaptopropyl)trialkoxysilanewith respect to silicon in the SBA-15; or (c) (3-mercaptopropyl)silanecovalently bound to a mesoporous silicate.
 7. The smoking article ofclaim 1, wherein the mercaptopropyl group is covalently bound toexterior and interior surfaces of the inorganic molecular sievesubstrate and wherein the inorganic molecular sieve substrate is amesoporous molecular sieve.
 8. The smoking article of claim 1, whereinthe sorbent is in granular form having a particle size from about 20mesh to about 60 mesh and/or the smoking article comprises from about 10mg to about 300 mg or from about 100 mg to about 200 mg of the sorbent.9. A cigarette filter comprising a sorbent having mercaptopropyl groupsbound to an inorganic molecular sieve substrate, wherein the sorbent iscapable of reducing the concentration of at least one heavy metalconstituent such as mercury and/or cadmium in mainstream smoke.
 10. Thecigarette filter of claim 9, wherein the inorganic molecular sievesubstrate (a) comprises mesoporous or microporous molecular sieves; (b)is selected from the group consisting of a zeolite, silicate,aluminophosphate, mesoporous silicate, mesoporous aluminosilicate, andmixtures thereof, or (c) comprises a zeolite selected from the groupconsisting of zeolite ZSM-5, zeolite A, zeolite X, zeolite Y, zeoliteK-G, zeolite ZK-5, zeolite Beta, zeolite ZK-4, and mixtures thereof. 11.The cigarette filter of claim 9, wherein the sorbent comprises (a)(3-mercaptopropyl)silane covalently bound to a zeolite; (b) SBA-15silica having incorporated therein up to about 15 mole percent of(3-mercaptopropyl)trialkoxysilane with respect to silicon in the SBA-15;or (c) (3-mercaptopropyl)silane covalently bound to a mesoporoussilicate.
 12. The cigarette filter of claim 9, wherein themercaptopropyl group is covalently bound to exterior and interiorsurfaces of the inorganic molecular sieve substrate and wherein themolecular sieve is a mesoporous molecular sieve.
 13. The cigarettefilter of claim 9, wherein the sorbent is in granular form having aparticle size from about 20 mesh to about 60 mesh and/or the cigarettefilter comprises from about 10 mg to about 300 mg or from about 100 mgto about 200 mg of the sorbent.
 14. The cigarette filter of claim 9,wherein the filter is selected from the group consisting of a monofilter, a dual filter, a triple filter, a cavity filter, a recessedfilter, and a free-flow filter.
 15. The cigarette filter of claim 9,wherein the filter comprises cellulose acetate tow, cellulose paper,mono cellulose, mono acetate, and combinations thereof.
 16. Thecigarette filter of claim 9, wherein the sorbent is incorporated intoone or more cigarette filter parts selected from the group consisting ofshaped paper insert, a plug, a space, cigarette filter paper, and afree-flow sleeve.
 17. The cigarette filter of claim 9, wherein thesorbent is incorporated with cellulose acetate fibers forming a plug ora free-flow filter element.
 18. The cigarette filter of claim 9, whereinthe sorbent is incorporated with polypropylene fibers forming a plug orfree-flow filter element.
 19. The cigarette filter of claim 9, whereinthe sorbent is incorporated in at least one of a mouthpiece filter plug,a first tubular filter element adjacent to the mouthpiece filter plug,and a second tubular filter element adjacent to the first tubularelement.
 20. The cigarette filter of claim 9, wherein the sorbent isincorporated in at least one part of a three-piece filter including amouthpiece filter plug, a first filter plug adjacent to the mouthpiecefilter plug, and a second filter plug adjacent to the first filter plug.21. A method of making a cigarette filter, the method comprisingincorporating a sorbent into a cigarette filter, wherein the sorbentcomprises mercaptopropyl groups bound to inorganic molecular sievesubstrate, and wherein the filter is a mono filter, a dual filter, atriple filter, a cavity filter, a recessed filter, or a free-flowfilter.
 22. A method of making a cigarette, the method comprising: (i)providing a cut filler to a cigarette making machine to form a tobaccocolumn; (ii) placing a paper wrapper around the tobacco column to form atobacco rod; and (iii) attaching the cigarette filter of claim 9 to thetobacco rod using tipping paper to form the cigarette.
 23. A method oftreating mainstream smoke comprising contacting mainstream tobacco smokewith a sorbent having at least one mercaptopropyl group bound to aninorganic molecular sieve substrate while drawing the smoke through asmoking article, wherein the sorbent reduces the concentration of atleast one heavy metal constituent such as mercury and/or cadmium inmainstream smoke.